The diversity of dog breeds is a unique phenomenon. Humans have managed to achieve many extreme changes in appearance and behavior through breeding. It is hard to believe that all of the approximately 550 dog breeds living today are closely related to the Asian gray wolf. However, the genes reveal even more: How did dog breeds originate and what relationships do they have? The author team of Udo Ganslosser, Yvonne Adler, and Gudrun Braun, from both science and practice, explain the molecular family trees of over 160 dog breeds and how they are genetically related. They address the heritability of behavior and personality and demonstrate what this means for breeding, health, education, and training. A fundamental work for breeders, trainers, and interested dog owners.